This invention is in the field of cutoff on stop and cutoff on overspeed devices for a turbojet and means of testing these two cutoff modes.
A turbojet necessarily has a device for cutting off the fuel supply directly from the pilot""s position in the aircraft on which the turbojet is fitted. This is a regulatory requirement.
This method of cutting off the turbojet is called cutoff on stop.
The set of equipment elements that contributes to operation of the cutoff on stop is called the cutoff on stop system.
Secondly, a turbojet must be fitted with a device to protect it against excessive rotation speeds (overspeed), particularly to prevent explosion of the turbine disks.
This is also a regulatory requirement.
This turbojet protection method is called the overspeed protection.
The set of hardware and software elements that contributes to operation of the overspeed protection is called the overspeed protection system.
Cutoff on stop is controlled from the pilot""s position in the aircraft by means of an engine stop handle called the master lever. The master lever may be the same as the throttle handle, the cutoff position then corresponding to a particular position of this handle.
The cutoff on overspeed is automatic and takes place after it is detected that the engine shaft rotation speed is greater than the maximum allowable rotation speed by a predetermined percentage.
The overspeed may be detected at the low pressure coupling and in this case we refer to the number of revolutions N1, or at the high pressure coupling and in this case we refer to the number of revolutions N2. Overspeed is detected by capturing a magnitude that varies with N1 or N2.
According to the regulations, cutoff on stop and cutoff on overspeed must be tested between landing and the next takeoff.
According to one known technique, the overspeed test is made by acting on the overspeed protection system that is tripped when the engine is stopped after landing. This is achieved by changing the trip value for this protection to a value of the rotation speed less than the engine idle speed, either using a computer controlling the engine, or mechanically by changing the setting of a spring. If the engine stops, correct operation of the overspeed protection system is demonstrated and it is thus tested after every flight.
The cutoff on stop system is verified during a maintenance operation.
The invention consists of modifying and adapting the architecture of the hydromechanical fuel regulator, the architecture of the logic of the engine regulation computer and the architecture of the turbojet overspeed detection boxes.
Thus, adaptation of the operating architecture and logic is a means of automatically testing that the entire overspeed system is operating correctly immediately before the turbojet is started.
It is also a way of testing operation of the cutoff on stop system when the turbojet is stopped after landing.
Consequently, the combination/optimization of the hydromechanical fuel regulator architecture with the architecture of the electronic system is a means of automatically and completely (100% coverage ratio) testing that the two systems (overspeed protection and cutoff on stop) are working correctly.
Thus, the invention relates firstly to a device for controlling and testing an aircraft engine cutoff on stop system, the engine comprising means of regulating the fuel flow input to engine injectors, these means calculating an allowable flow of fuel to sensors determining the value of the real instantaneous flow value input to engines, a means of closing the fuel inlet to engine injectors that is normally open and closes under the action of controllable actuation means, the device being characterized in that the engine cutoff on stop is obtained by pulling a master lever that can be manually moved from a first position into a second position, the changeover to this second position actuating means of closing off the fuel supply, and in that the correct operation test of this cutoff on stop consists of measuring the difference between the fuel flow authorized by the engine regulation means and the real fuel flow measured by sensors determining the real instantaneous flow value.
The invention also relates to an overspeed protection device for an aircraft engine, the engine comprising means of regulating the fuel flow input to the engine injectors, these means calculating an allowable fuel flow as a function of the engine rotation speed and external parameters, sensors sensing the real value of the instantaneous flow input to engines, a means of closing the fuel flow into the engine injectors, this means being normally open and closing under the action of controllable actuation means, means of measuring the instantaneous rotation speed of the engine, means of fixing instantaneous rotation speed thresholds that constitute detection of an overspeed if exceeded, a first threshold forming the overspeed in test threshold, and a second threshold forming the real overspeed threshold, device characterized in that the real overspeed or the test overspeed is detected in a logic electronic module into which a magnitude is input representing the value of the real instantaneous rotation speed of the engine, this module comprising a state switch that can be in at least two states, a test state and a normal state, this module making a comparison between the real rotation speed and the test overspeed threshold when the state switch is in the test state, and between the real rotation speed and the real overspeed threshold, when the state switch is in the normal state, this module outputting a closing command to the means of actuating the fuel inlet closing device, and in that the correct operation test of engine cutoff on overspeed consists of measuring the difference between the fuel flow authorized by engine control means and the real fuel flow measured by the sensors of the real value of the instantaneous fuel flow sensors.